1. Field of the Invention
The present invention relates to a semiconductor device.
2. Description of Related Art
In a semiconductor device, a plurality of wiring layers are formed on a semiconductor substrate on which a functional circuit with high power consumption, such as a CPU (Central Processing Unit), a ROM (Read Only Memory), or a RAM (Random Access Memory), is formed. A power supply wire is formed at each wiring layer, and the power supply wires of the wiring layers are electrically connected to each other through vias. The power supply wire at the wiring layer serving as the bottom layer is electrically connected to the functional circuit via a contact hole. A power supply pad is electrically connected to the power supply wire at the wiring layer serving as the top layer. Power is supplied from the power supply pad to the functional circuit through the power supply wires of the wiring layers. In this case, a voltage drop tends to increase with an increase in the distance from the power supply pad when viewed from a planar perspective. In other words, the semiconductor device has, e.g., the problem of a low capability for supplying power to a substantially center portion of the functional circuit which is far from the power supply pad when viewed from the planar perspective.
For this reason, the semiconductor devices in Patent Documents 1 and 2 each have a reinforcement power supply wire to reinforce a portion where the semiconductor device has a large voltage drop and has a low power supply capability. More specifically, in the semiconductor device of each of Patent Documents 1 and 2, a power supply pad is electrically connected to a ring wire. One end of the reinforcement power supply wire is electrically connected to the ring wire. The other end of the reinforcement power supply wire extends to, e.g., a substantially center portion of a functional circuit which is the portion where the semiconductor device has a low power supply capability and is electrically connected to the substantially center portion. The ring wire and the power supply pad are formed at different layers. The ring wire and the power supply pad are connected through a via.
Note that the semiconductor device in Patent Document 2 is configured such that the width dimension of the reinforcement power supply wire is changed depending on the distance from the power supply pad to a portion where the semiconductor device has a low power supply capability when viewed from a planar perspective.    [Patent Document 1] Japanese Patent Application Laid Open No. 61-193467    [Patent Document 2] Japanese Patent Application Laid Open No. 2006-313765